A tumor cell exists in part because it has selected for one or more mutations that allows it to partially or completely escape immune surveillance in vivo.
In an attempt to elicit an immune response to a tumor cell, previous researchers have used dendritic cells, which are professional antigen-presenting cells, to present tumor antigens to the immune system. For example, dendritic cells pulsed with peptide or tumor lysate have been used to vaccinate melanoma patients.
However, simply presenting tumor antigens to the immune system in the foregoing manner has not been effective because such antigens were merely endocytosed by the dendritic cells and generally presented through the Major Histocompatibility Complex (MHC) class II, which elicits only helper T cells and does not provide a robust immune response.
In contrast, presenting tumor antigens via the MHC class I pathway contributes to a more robust anti-tumor immunity by activating CD8+ T cells. Previous researchers have attempted to present tumor antigens through the MHC class I pathway by using gene transfer methods. However, these methods have disadvantages, including (1) a limited ability to identify all of the important tumor-specific antigens, (2) a limited ability to map the genes of specific tumor antigens, (3) only one or a small number of known tumor antigen genes can be introduced into a dendritic cell and (4) the methods are time-consuming and cumbersome.